1. Field of the Invention
This invention relates to a magnetic tunnelling element in which a pair of magnetic layers are laminated via a tunnel barrier layer and in which the tunnel current is caused to flow from one to the other magnetic layer, with the conductance of the tunnel current being changed in dependence upon the ratio of polarization of magnetization of the paired magnetic layers. This invention also relates to a method for manufacturing the magnetic tunnelling element.
2. Description of the Related Art
It has been reported that, if, in a layered structure comprised of a thin insulating layer sandwiched between a pair of magnetic metal layers, a pre-set voltage is applied across the paired magnetic metal layers as electrodes, a magnetic tunnelling effect is displayed, in which the conductance of the tunnel current flowing in the insulating layer is changed in dependence upon the relative angle of magnetization of the paired magnetic metal layers. That is, a layered structure comprised of a thin insulating layer sandwiched between a pair of magnetic metal layers exhibits a magneto-resistance effect with respect to the tunnel current flowing in the insulating layer.
In this magnetic tunnelling effect, the specific magnetoresistance can be theoretically calculated based on the ratio of polarization of magnetization of the paired magnetic metal layers. In particular, if Fe is used as the material of the paired magnetic metal layers, expectation may be made of the specific magnetoresistance amounting approximately to 40%.
Therefore, a magnetic tunnelling element having a layered structure comprised of a thin insulating layer sandwiched between paired magnetic metal layers is stirring up notice as an element for detecting an external magnetic field.
In the above-described magnetic tunnelling element, a metal oxide is routinely used as the thin insulating layer. However, if a metal oxide is used as an insulating layer, pinholes etc tend to be formed, such that shorting tends to be induced between the paired magnetic metal layers. There are occasions wherein, if a metal oxide is used as an insulating layer, the metal oxidation degree is insufficient, such that the tunnel barrier is incomplete such that the magnetic tunnelling effect is not displayed.
In the conventional magnetic tunnelling element, changes in conductance of the current in dependence upon the relative angle of magnetization of the paired magnetic metal layers, laminated via an insulating layer in-between, that is the magnetic tunnelling effect, were detected. However, with the conventional magnetic tunnelling element, it is difficult to demonstrate the magnetic tunnelling effect reliably such that the conventional magnetic tunnelling element cannot be used for practical application.